Sound insulation/absorption structure, and structure having these applied thereto

ABSTRACT

A sound insulation/absorption structure, a sound insulation/absorption device, and a structure having these applied thereto and a member constituting the same, are capable of insulating or absorbing sound by stiffness control. The sound insulation/absorption structure comprises a film member, such as a polymer film or metal foil, and a frame body having at least one annular opening, the film member being fixed to the frame body, the section of the film member surrounded by the frame body being of a curved shape such as a dome, wherein the resonance frequency of the in-plane stretching of this curved shape is set at a frequency equal to or higher than the audible frequency band, so as to insulate or absorb sound by the elastic force of the film. The film member may be replaced by an acrylic, polyethylene terephthalate or other plastic plate, an aluminum or other metal plate, or a veneer or other plate member, molded into a curved shape, such as a dome, a semi-cylinder and a cone.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a sound insulation/absorptionstructure, a sound insulation/absorption device, and a structure havingthese applied thereto and a member constituting the same, which insulatesound by elastic repulsion or absorb the sound by an elastic loss.

2. Description of the Prior Art

The sound insulation performance of a single layer wall improves inproportion to the increasing amount of mass. Thus, a material with largemass, such as a concrete wall, a block wall, a bonded brick wall, lead,and a steel plate, is used to insulate a sound. A sound transmissionloss is used as an index to show the sound insulation performance of awall. The sound transmission loss TL of the single layer wall in thecase where the sound is vertically incident on the wall surface isexpressed by the following formula (1): $\begin{matrix}{{TL} = {10\quad{\log_{10}\left\lbrack {\left( {\frac{r}{2\rho_{0}c_{0}} + 1} \right)^{2} + \left( \frac{{\omega\quad m} - {Y/\omega}}{2\rho_{0}c_{0}} \right)^{2}} \right\rbrack}}} & (1)\end{matrix}$where ω is an angular frequency, ρ₀ is the density of air, c₀ is thesound velocity of air, r is the viscous resistance of the wall in thethickness direction, m is the mass of the wall, and y is the elasticconstant of the wall in the thickness direction.

FIG. 16 shows the sound transmission loss TL obtained by the formula (1)relative the thickness direction shown in the following formula (2):$\begin{matrix}{f_{r} = {\frac{1}{2\quad\pi}\sqrt{\frac{Y}{m}}}} & (2)\end{matrix}$

The sound transmission loss TL is proportional to the frequency in 6dB/oct on the higher frequency side than the resonance frequency fr.This area results from a term including the mass of the formula (1) andis referred to as a mass law.

On the other hand, the sound transmission loss TL is inverselyproportional to the frequency in −6 dB/oct on the lower frequency sidethan the resonance frequency fr. This area results from a term includingan elastic constant of the formula (1) and is generally referred to asstiffness control.

In a conventional technique, the resonance frequency fr is provided in alow frequency area. Since the sound insulation performance of a soundinsulation wall in an audible area depends on the mass law, the soundinsulation performance of the wall deteriorates in proportion to lowfrequency sound. The sound insulation performance can be improved byincreasing the thickness (a surface density), but the increase of thesound transmission loss is 6 dB at most even by doubling the thickness.It is also said that a film or plate with a small surface density hardlyever has the sound insulation performance. On the other hand, a sound ofa lower frequency than the resonance frequency fr can be insulated intheory by the action of the wall elasticity.

Thus, problems are pointed out in the conventional sound insulationmethod whereby the sound insulation performance deteriorates inproportion to low frequency sound and there is a limit to the necessarysteps which can be taken to improve the sound insulation especially incollective housing or transport facilities because the sound insulationperformance depends in collective housing or transport facilitiesbecause the sound insulation performance depends on the surface density.

Since the sound insulation method using stiffness control does notdepend on the mass, it is not only possible to take proper soundinsulation steps at the places where sound insulation steps could not betaken in the past, but also sound insulation for the low frequency soundcan be expected. However, a sound insulation/absorption structure usingstiffness control has not been in practical use as yet.

As a sound insulation/absorption structure for bringing stiffnesscontrol into view, a sound insulation structure and a soundinsulation/absorption complex structure are known, which comprise aframe body, surface materials provided on both sides of the frame body,and a sound absorption material filled within these surface materials,wherein each surface material is formed to have a curved surface shapeto increase the stiffness (rigidity) so that the stiffness area in thetransmission loss frequency characteristics reaches a frequency higherthan the resonance transmission frequency determined by the surfacedensity of the surface material and the spacing of the surface materials(e.g., refer to Japanese Patent Application Publication No. 5-94195).

Further, a sound insulation structure is known, which comprises a framebody, surface materials provided on both sides of the frame body, and asound absorption material filled between these surface materials,wherein the surface materials are curved to increase the stiffness(rigidity) by pressurizing or depressurizing a space surrounded by theframe body and the surface materials. Sound insulation loss (deficiency)by the resonance transmission is prevented by controlling the vibrationsof the surface materials (e.g., refer to Japanese Patent ApplicationPublication No. 6-161463).

A variable sound absorption device is also known, which comprises apiezoelectric material having piezoelectric properties of which theouter periphery is secured, a pair of electrodes provided on bothopposite faces of this piezoelectric material, and a negativecapacitance circuit adapted to connect between these electrodes, whereinthe piezoelectric material is in a curved flat state and the electricproperties of the negative capacitance circuit is constituted to bevariable, thereby changing an elastic constant and a loss factor of thepiezoelectric material (e.g., refer to Japanese Patent ApplicationPublication No. 11-161284).

However, the inventions disclosed in Japanese Patent ApplicationPublication Nos. 5-94195 and 6-161463 refer to a technique to controldeformation from a surface friction, in other words, a soundtransmission caused by a bending resonance of a sound insulation wall asa result of increasing stiffness, a so-called coincidence, wherein theresonance frequency of this bending is due to the surface friction seenin a mass control domain in addition to the resonance frequency fr inthe thickness direction as described above. Accordingly, to attain soundinsulation by stiffness control, it is necessary to discuss theresonance frequency fr, that is, the surface density and the elasticityof the in-plane stretching. However, these inventions do not deal withthe resonance frequency fr and thus, our problems can not be solved.

Further, the invention disclosed in Japanese Patent ApplicationPublication No. 11-161284 describes in theory that if the film iscurved, the attenuation of sound can be increased. However, thisinvention does not describe that the sound insulation by elasticrepulsion (stiffness control) of the film can be attained in less thanthe resonance frequency f r and the sound insulation performance dependson the mass of the film, the length of the periphery, the elasticconstant, and the tensile force. The invention does not describe a soundinsulation/absorption structure taking these into consideration. Thus,our problems cannot be solved.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to overcome theabove-mentioned problems in the conventional technology and to provide asound insulation/absorption structure, a sound insulation/absorptiondevice, and a structure having these applied thereto and a memberconstituting the same.

To overcome the above-mentioned problems, according to the invention ofclaim 1, a film member such as a polymer film and a metal foil is formedinto a curved shape such as a dome, a barrel, and a cone, the peripheryof this curved shape is fixed to another structure, and the resonancefrequency of the curved shape in the in-plane stretching is set at afrequency equal to or higher than the audible frequency band to insulateor absorb sound by the elastic force of the film.

By securing the film member directly to the structure, it is possible toinsulate or absorb the sound by stiffness control.

The invention according to claim 2 comprises a film member, such as apolymer film and a metal foil, and a frame body having at least oneopening of a lattice shape, a honeycomb shape or an annular shape,wherein the film member is fixed to the frame body, the section of thefilm member surrounded by the frame body is formed into a curved shapesuch as a dome, a barrel, and a cone, and the resonance frequency of thecurved shape in the in-plane stretching is set at a frequency equal toor higher than the audible frequency band, thereby insulating orabsorbing sound by the elastic force of the film.

In this manner, the invention comprises the light film member and theframe body having at least one opening of a lattice, honeycomb orannular shape, wherein the periphery of the film member is secured bythe frame body, the section of the film member surrounded by the framebody is formed into a curved shape such as a dome and a barrel, and theresonance frequency of the section in the in-plane stretching vibrationis set at a frequency equal to or higher than the audible frequencyband, thereby being capable of insulating or absorbing sound bystiffness control.

The invention of claim 3 refers to a sound insulation/absorptionstructure according to claim 1 or claim 2 in which a holding means isprovided to hold the film member in the curved shape.

In this manner, the tensile force and the curved shape such as a domecan be applied to the film member by the holding means for holding andthus, sound insulation or absorption by stiffness control can beconducted.

The invention of claim 4 refers to the sound insulation/absorptionstructure according to claim 1 or claim 2 in which the tensile force isapplied to the film member.

By applying the tensile force to the film member, it is possible toeffectively insulate or absorb sound by stiffness control.

The invention of claim 5 refers to the sound insulation/absorptionstructure according to claim 1 or claim 2 in which the film member isreplaced by a plate member, such as a plastic plate, a metal plate and aveneer board (plate), formed into a curved shape such as a dome, abarrel and a cone.

In this manner, the sound insulation/absorption structure comprises alight plate member, and a frame body having at least one opening of alattice, honeycomb or annular shape, wherein the periphery of the platemember is secured by the frame body, the section of the plate membersurrounded by the frame body is formed into a curved shape such as adome and a barrel, the resonance frequency of the section in thein-plane stretching vibration is set at a frequency equal to or higherthan the audible frequency band, thereby being capable of insulating orabsorbing sound by stiffness control.

The invention of claim 6 comprises a film member, a frame body, anelastic body, and a supporting plate, wherein the elastic body and thefilm member are placed on the supporting plate to be pressed with theframe body so that the elastic body and the film member are held betweenthe frame body and the supporting plate to apply a tensile force to thefilm member, the film member is formed into a curved shape such as adome, and the resonance frequency of the curved shape in the in-planestretching is set at a frequency equal to or higher than the audiblefrequency band to insulate or absorb sound by the elastic force of thefilm.

As described above, the elastic body and the film member are placed onthe supporting plate to be pressed with the frame body so that theelastic body and the film member are held between the frame body and thesupporting plate to apply the tensile force to the film member, the filmmember is formed into the curved shape such as a dome, and the resonancefrequency of the curvature-having shape in the in-plane stretching isset at a frequency equal to or higher than the audible frequency band,thereby being capable of insulating or absorbing sound by stiffnesscontrol.

The invention of claim 7 comprises two film members, a frame body, andan elastic body, wherein the elastic body is placed between the two filmmembers, the elastic body and the two film members are held between theframe body to apply a tensile force to the two film members, the twofilm members are formed into a curved shape such as a dome, and theresonance frequency of the curved shape in the in-plane stretching isset at a frequency equal to or higher than the audible frequency band toinsulate or absorb sound by the elastic force of the film.

In this manner, the elastic body is placed between the two film members,the elastic body and the two film members are further held between theframe body to apply the tensile force to the two film members, the twofilm members are formed into the curved shape such as a dome, and theresonance frequency of the curved shape in the in-plane stretching isset at a frequency equal to or higher than the audible frequency band,thereby being capable of insulating or absorbing sound by stiffnesscontrol.

The invention of claim 8 according to any one of claims 1 through 7refers to the sound insulation/absorption structure, wherein the filmmember formed into the curved shape or the plate member formed into thecurved shape is set in a one or two-dimensional array.

With this arrangement, by setting the film member formed into the curvedshape or the plate member formed into the curved shape in a one ortwo-dimensional array, it is possible to form a soundinsulation/absorption structure which extensively insulates or absorbssound by stiffness control.

The invention of claim 9 according to any one of claims 1 through 8refers to the sound insulation/absorption structure, wherein the surfacedensity, elastic constant, outer peripheral dimensions, and curvatureradius of the curved section of the film member or the plate member isset so that the resonance frequency in the in-plane stretching vibrationis within or higher than the audible frequency band.

The invention of claim 10 according to any one of claims 1 through 9refers to the sound insulation/absorption structure, wherein the filmmember or the plate member and the frame body securing these areintegrally formed.

In the invention of claim 11, the film member or the plate memberconstituting the sound insulation/absorption structure according to anyone of claims 1 through 10 is provided with a piezoelectric member towhich a circuit presenting a negative capacitance is connected.

By connecting the circuit presenting the negative capacitance to thepiezoelectric member attached to the film member or the plate member, itis possible to constitute a sound insulation/absorption device which canelectrically control the sound insulation/absorption performance.

In the invention of claim 12, the film member or the plate memberconstituting the sound insulation/absorption structure according to anyone of claims 1 through 10 is a member with piezoelectric properties towhich a circuit presenting a negative capacitance is connected.

By connecting the circuit presenting the negative capacitance to thefilm member or the plate member having the piezoelectric properties, itis possible to constitute a sound insulation/absorption device which canelectrically control the sound insulation/absorption performance.

In the invention of claim 13, the sound insulation/absorption structureaccording to any one of claims 1 through 10 is applied to structuressuch as an automobile, a vehicle such as an electric train, an aircraft,a marine vessel and other transport equipment (vehicle), a panel,partition and other building material, a sound insulation wall, asound-proof wall, a building structure, a chamber, electric equipment, amachine, acoustic equipment and the like to insulate or absorb sound.

In the invention of claim 14, the sound insulation/absorption structureaccording to any one of claims 1 through 10 is applied to a memberconstituting the structures such as an automobile, a vehicle such as anelectric train, an aircraft, a marine vessel and other transportequipment (vehicle), a panel, a partition and other building material, asound insulation wall, a sound-proof wall, a building structure, achamber, electric equipment, a machine, acoustic equipment and the liketo insulate or absorb sound.

In the invention of claim 15, the sound insulation/absorption deviceaccording to claim 11 or claim 12 is applied to structures such as anautomobile, a vehicle such as an electric train, an aircraft, a marinevessel and other transport equipment (vehicle), a panel, a partition andother building material, a sound insulation wall, a sound-proof wall, abuilding structure, a chamber, electric equipment, a machine, acousticequipment and the like to insulate or absorb sound.

In the invention of claim 16, the sound insulation/absorption deviceaccording to claim 11 or claim 12 is applied to a member constitutingthe structures such as an automobile, a vehicle such as an electrictrain, an aircraft, a marine vessel and other transport equipment(vehicle), a panel, a partition and other building material, a soundinsulation wall, a sound-proof wall, a building structure, a chamber,electric equipment, a machine, acoustic equipment and the like toinsulate or absorb sound.

BRIEF DESCRIPTION THE DRAWINGS

FIG. 1 shows a first embodiment of a sound insulation/absorptionstructure according to the present invention, wherein FIGS. 1 (a) and 1(b) are the front view and the cross-sectional view thereof,respectively;

FIG. 2 shows a second embodiment of the sound insulation/absorptionstructure according to the present invention, wherein FIGS. 2 (a) and 2(b) are the front view and the cross-sectional view thereof,respectively;

FIG. 3 is a cross-sectional view of a third embodiment of the soundinsulation/absorption structure according to the present invention;

FIG. 4 is a cross-sectional view of a fourth embodiment of the soundinsulation/absorption structure according to the present invention;

FIG. 5 is a cross-sectional view of a fifth embodiment of the soundinsulation/absorption structure according to the present invention;

FIG. 6 is a cross-sectional view of a sixth embodiment of the soundinsulation/absorption structure according to the present invention;

FIG. 7 is a cross-sectional view of a seventh embodiment of the soundinsulation/absorption structure according to the present invention;

FIG. 8 shows a schematic diagram of an electric circuit presenting anegative capacitance, wherein FIG. 8 (a) shows the case where apiezoelectric body and the negative capacitance are connected inparallel and FIGS. 8 (b) and (c) show the cases where the piezoelectricbody and the negative capacitance are series-connected;

FIG. 9 is a schematic diagram of the piezoelectric body and elementswhich are connected to a negative capacitance circuit;

FIG. 10 shows the frequency characteristics of a sound transmission lossof which the parameter is the curvature radius of a polymer film;

FIG. 11 shows the frequency characteristics of a sound transmission lossof which the parameter is the thickness of the polymer film;

FIG. 12 shows the frequency characteristics of an insertion loss of thesound insulation/absorption structure;

FIG. 13 shows the frequency characteristics of a sound transmission lossof a panel in which a rigid plastic molded into a dome shape is used;

FIG. 14 shows the frequency characteristics of a sound transmission lossin the case where a PVDF film is controlled by a negative capacitancecircuit;

FIG. 15 shows the frequency characteristics of a sound transmission lossof a large panel in which a rigid plastic of a dome shape is set in atwo-dimensional array; and

FIG. 16 is a graph showing the sound transmission loss relative to alogarithmic frequency.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments of the present invention will be describedhereunder with reference to the accompanying drawings (FIGS. 1 through15).

A sound insulation/absorption structure according to the presentinvention comprises a light film or plate member, formed into a curvedshape such as a dome and a barrel, which has been considered to have alesser sound insulation performance in the past, and a frame bodyadapted to secure its periphery. The film or plate member has lessstrain by sound pressure in a flat shape and has little sound insulationperformance by elasticity and little sound absorption performance by anelastic loss.

However, when the film or plate member is formed into a curved shapesuch as a dome and a barrel, it begins to produce the in-planestretching vibration increasing or decreasing the curvature by soundpressure. By causing the film or plate member to produce the in-planestretching vibration by sound pressure, sound insulation of the film orplate member by elasticity and sound absorption by elastic loss arepossible.

Sound insulation by the film member formed into the dome shape or thelike is attained at a lower frequency band than the resonance frequencyfr of the in-plane stretching vibration. If the lighter film member withlarger elastic constant is used according to the formula (2), it ispossible to easily set the resonance frequency fr at a frequency higherthan the audible frequency band. Since the resonance frequency frdepends on the curvature radius of the film, thickness of the filmmember, tensile force applied to the film member, and length of thesection secured by the frame body, it is necessary to properly fix theseto set the resonance frequency fr at the intended frequency.

A sound transmission loss TL and a sound absorption coefficient α of thefilm member of which the periphery is secured and to which a curvaturehas been applied is given by the following formulas (3) through (5):$\begin{matrix}{{TL} = {10\quad{\log_{10}\left\lbrack {1 + \frac{Y^{''}}{\omega\quad\zeta} + \frac{\left( Y^{''} \right)^{2} + \left( {Y^{\prime} - {\rho\quad\omega^{2}R^{2}}} \right)^{2}}{\left( {2\quad\omega\quad\zeta} \right)^{2}}} \right\rbrack}}} & (3) \\{\alpha = \frac{4\quad\zeta\quad\omega\quad Y^{''}}{\left( {Y^{\prime} - {\rho\quad\omega^{2}R^{2}}} \right)^{2} + \left( {Y^{''} + {\omega\quad\zeta}} \right)^{2}}} & (4) \\{\zeta = {\rho_{0}c_{0}{R^{2}/h}}} & (5)\end{matrix}$

where Y′ is the in-plane elastic constant of the film member, Y″ is thein-plane elastic loss of the film member, ω is the angular frequency, ρis the density of the film member, h is the thickness of the filmmember, R is the curvature radius of the film member, ρ₀ is density ofair, and c₀ is the sound velocity of air.

According to the formulas (3) through (5), the sound transmission lossTL and the sound absorption coefficient α become minimal when the filmmember is in a flat shape (R=∞) and increase as R becomes smallerbecause the sound transmission loss TL and the sound absorptioncoefficient α are in inverse proportion to R.

The sound insulation/absorption structure according to the presentinvention provides an optimum structure, material and technique toembody the above-mentioned principle as a sound insulation structurewhich requires a large area and combines a frame body rigid relative tosound and a film or plate member provided with curvature. In the casewhere the frame body has a flat shape, flexure (deflection) may becaused in the frame body itself depending on the sound to decrease thesound insulation performance. By bending the frame body, the flexure ofthe frame body by the sound can be reduced so as to prevent thedeterioration of the sound insulation performance.

As shown in FIG. 1, a first embodiment of a sound insulation/absorptionstructure according to the present invention comprises a film member 1formed into a domed shape with a curvature and an annular frame body 2adapted to secure the film member 1 by securing the edge section of thefilm member 1 between both sides of the frame body 2. A metal foil suchas an aluminum foil, a polymer film such as a polyethylene film or thelike is used as the film member 1. The shape of the film member 1 ofwhich the edge section is secured by the frame body 2 can not only be adome shape, but also a shape with curvature such as a barrel and a cone.On the other hand, the frame body 2 can not only be an annular shape,but also a square (lattice) shape, a hexagonal (honeycomb) shape and thelike. The frame body 2 can be made of plastics, metal and the like.

The film member can be replaced by a plastic plate such as an acrylicand a polyethylene terephthalate, a metal plate such as aluminum or aplate member such as a veneer board, formed into a curved shape such asa dome, a barrel, and a cone.

As shown in FIG. 2, a second embodiment of the soundinsulation/absorption structure can also be composed of a film member 3having a curved shape such as a dome formed at four places and asquare-shaped (lattice-shaped) frame body 4 adapted to secure the filmmember 3 by holding the periphery of each curved shape between bothsides thereof. It is to be noted that the number of curved shapes suchas the dome formed on the film member 3 can not be limited to four, buta plurality of curved shapes can be provided. In this case, the framebody 4 can be formed to meet the number of curved shapes such as thedome formed on the film member 3.

In a third embodiment of the sound insulation/absorption structure asshown in FIG. 3, a metal mesh 5 serving as a holding means is formed ina dome or barrel shape. The film member 1 held between both sides of theannular frame body 2 is applied to the metal mesh 5, wherein the tensileforce and the curved shape such as the dome are applied to the filmmember 1.

A fourth embodiment of the sound insulation/absorption structure asshown in FIG. 4 is provided, in which a plurality of metal meshes 5 isformed in a dome shape and a film member 3 held between both sides of aframe body 4 of a lattice shape is applied to the metal mesh 5 so thatthe tensile force and the curved shape such as the dome are applied tothe film member 3.

Referring to a fifth embodiment of the sound insulation/absorptionstructure as shown in FIG. 5, an elastic body 6 such as sponge servingas a protective layer is provided between the film member 1 and themetal mesh 3 in the third embodiment.

A sixth embodiment of the sound insulation/absorption structure isprovided as shown in FIG. 6, in which an elastic body 6 and a filmmember 3 are put on a supporting plate 7 to be pressed by alattice-shaped frame body 4 so that the elastic body 6 and the filmmember 3 are held between the frame body 4 and the supporting plate 7,wherein the tensile force is applied to the film member 3 formed into acurved shape such as a dome.

Referring to a seventh embodiment of the sound insulation/absorptionstructure as shown in FIG. 7, the elastic body 6 is held between twofilm members 1 and the elastic body 6 and the two film members 1 arethen held between the frame body 2 to apply the tensile force to the twofilm members 1, wherein the two film members 1 are formed into a curvedshape such as a dome.

In this case, a sound absorption effect can be added if a material withsound absorption power (a sound absorption material) such as glass wooland rock wool is used. The film member 1 can be replaced by a platemember such as a plastic plate, a metal plate and a veneer board, formedinto a curved shape such as a dome and a barrel.

In any sound insulation/absorption structure as shown in FIGS. 1 through7, the sound insulation performance and the sound absorption performancedepend on the resonance frequency fr of the sections of the film members1 and 3 surrounded by the frame bodies 2 and 4 in the in-planestretching vibration. It is therefore important to set the surfacedensity and elastic constant of the film members 1 and 3, and thelength, curvature radius, and tensile force of the sections surroundedby the frame bodies 2 and 4 so that this resonance frequency is set at afrequency equal to or higher than the audible frequency band.

Further, if a material with piezoelectric properties (i.e., apiezoelectric body) is used as the film members 1 and 3 constituting thesound insulation/absorption structure, an electrode is provided on eachside of the piezoelectric material, and an electric circuit presenting anegative capacitance (i.e., negative capacitance circuit) is connectedin such an equivalent manner that a condenser having a negativecapacitance is connected in parallel or in series, it is possible toconstitute a sound insulation/absorption device which can artificiallychange the sound insulation performance and the sound absorptionperformance by electrically changing the elastic constant of the filmmembers 1 and 3.

Available as the piezoelectric body is a piezoelectric polymer such as apolyvinylidene fluoride, a vinylidene fluoride copolymer, a polylacticacid, and cellulose; piezoelectric ceramics such as PZT; or a compositematerial of the piezoelectric material and the polymer material.

FIG. 8 shows negative capacitance circuits 8 a, 8 b and 8 c. In thenegative capacitance circuit 8 a as shown in FIG. 8 (a), the elasticconstant of the piezoelectric body 9 can be increased, while in thenegative capacitance circuits 8 b and 8 c as shown in FIGS. 8 (b) and(c), the elastic constant thereof can be decreased. Even in the casewhere any negative capacitance circuit 8 a, 8 b or 8 c is connected, theelastic constant of the piezoelectric body 9 changes at a frequency inwhich the electric loss of the piezoelectric body 9 and the negativecapacitance circuits 8 a, 8 b and 8 c substantially agree.

An element Z0 as shown in FIG. 8 is formed by a resistor and acondenser. In this case, if a condenser made of the same material as thepiezoelectric material is used, it is possible to uniformly change theelastic constant of the piezoelectric body 9 irrespective of thefrequency. Elements Z1 and Z2 as shown in FIGS. 8 (a) through (c) areconstituted by at least one of a resistor, a condenser and a coil. Thecapacitance of the negative capacitance circuits 8 a and 8 b as shown inFIGS. 8 (a) and (b) is expressed by a product of the capacitance of theelement Z0 and the impedance ratio (Z2/Z1) of the elements Z2 and Z1.

In the negative capacitance circuit 8 c as shown in FIG. 8 (c), anelement expressed by −Z3×Z5/Z4 is connected in parallel with the elementZ0. The capacitance of the negative capacitance circuit 8 c is expressedby a product of the capacitance, in which the element expressed by−Z3×Z5/Z4 is connected in parallel with the element Z0, and theimpedance ratio (Z2/Z1). If the elements Z1 and Z2 are constituted byone variable resistor, it is possible to make the capacitance of thenegative capacitance circuits 8 a, 8 b and 8 c variable.

As shown in FIG. 9, elements 11, 12 and 13 are connected to thepiezoelectric body 9 which is connected to the negative capacitancecircuits 8 a, 8 b and 8 c. The elements 11 through 13 can be constitutedby at least one of a resistor, a condenser, and a coil, or by openingthe element 11, the elements 12 and 13 can also be short-circuited.

An evaluation result of the sound insulation characteristics on thesound insulation/absorption structure according to the present inventionis shown in FIG. 10. A vertically incident transmission loss wasmeasured, using a sound tube, for a polymer film having a flat shape andpolymer films with a curvature radius of 10 cm or 5 cm, to which a metalmesh is applied from behind.

In the case of the flat polymer film, the sound transmission loss isseveral dB and the polymer film does not demonstrate a sound insulationperformance. However, in the case of the polymer film with a curvatureradius of 10 cm, the sound transmission loss increases more than 10˜20dB and shows a tendency to increase in response to the low frequencypeculiar to the stiffness control.

As a result of changing the curvature radius of the polymer film from 10cm to 5 cm, the sound transmission loss further increased by about 5 dB.In this manner, when the curvature is applied to the polymer film, thefilm begins to show the sound insulation performance of stiffnesscontrol and the sound insulation performance increases as the curvatureradius becomes smaller.

Next, frequency characteristics of the sound transmission loss in apolymer film of a thickness of 12 microns, 40 microns, and 80 microns,which is formed into a dome shape and to which tensile force is appliedare shown in FIG. 11. The sound transmission loss increases as thethickness of the polymer film increases.

Next, a polymer film is secured to a frame body in which a squarelattice of 2.5 cm×2.5 cm is arranged 10×10 in every direction and ametal mesh formed into a dome shape is pressed into a polymer filmsurrounded by each lattice to form the polymer film in a dome shape. Thedomed polymer film is then disposed in a two-dimensional manner toprovide a sound insulation/absorption structure. An insertion loss ofthe sound insulation/absorption structure formed in this manner wasmeasured using a small reverberation box. In addition, an evaluation wasalso made on the sound insulation/absorption structure to which flatveneer boards with a thickness of 1 cm each are laminated to provide adouble wall.

FIG. 12 shows the evaluation result. An insertion loss of the soundinsulation/absorption structure according to the present invention showsa tendency to become larger as the frequency peculiar to the stiffnesscontrol lowers. On the other hand, the insertion loss of the veneerboard shows a tendency to become larger as the frequency peculiar to themass law becomes higher. In the double wall having these combined, aninsertion loss of more than 20 dB was obtained between 100 Hz and 20kHz.

FIG. 13 is a graph showing the sound insulation performance of a panelusing a rigid plastic formed into a dome shape, relative to thefrequency. A rectangular opening of 14 cm×24 cm is provided at thecenter of a rectangular aluminum plate (1 cm thick) of 20 cm×30 cm and apolyethylene terephthalate (PET) plate with a thickness of 1.5 mm formedinto a dome shape with a height of 3 cm is inserted into the opening.The periphery of the plate is held and secured between two aluminumframes from both directions.

In the case of more than 1 kHz, the sound insulation performanceimproves as the frequency becomes higher. In other words, a tendency ofsound insulation by a so-called mass of plate can be seen. On the otherhand, in the case of less than 1 kHz, a tendency of frequency dependencecan not be seen in the sound insulation performance and a result wherebythe sound insulation performance becomes constant at about 30 dB wasobtained. This is because the sound insulation acts from elasticity ofthe plastic plate formed into a dome shape.

FIG. 14 shows the result of sound insulation performance control inwhich the plastic plate of the panel is PVDF (polyvinylidene fluoride)film and is controlled by the negative capacitance circuit. Since theelastic force of the film is small as compared to the rigid plastic, theresonance frequency of the in-plane stretching vibration moves to thelower frequency side. The film's original sound insulation performanceshows the effect by the mass in the case of more than 300 Hz. In thecase of less than 300 Hz, there is a tendency for the sound insulationperformance to increase in response to the low frequency peculiar to theelastic effect. The sound insulation performance of the panel increasedup to 20 dB between 100 Hz and 1 kHz by the circuit control.

FIG. 15 shows frequency characteristics of the sound insulationperformance of a large panel in which a dome-shaped rigid plastic isdisposed in a two-dimensional manner. The outer peripheral dimensions ofthe panel are about 1.2 m×1.6 m. A PET plate with a thickness of 1.5 mmformed into a square of 4 cm×4 cm and a dome shape of a curvature radiusof 4 cm was arranged on the panel in a two-dimensional manner. The domeshape was disposed at 15 locations to be 5 lines×3 rows on the PET plateof a size of 20 cm×30 cm and each dome shape is secured by an aluminumframe. This is one unit, and 30 additional units of the dome shapes werefurther disposed to have 6 lines×5 rows. The large panel demonstrated asound insulation performance of more than 20 dB was maintained between100 HZ and 1 kHz.

These results indicate that the present invention can provide a soundinsulation structure which realizes sound insulation by the elasticforce of the domed film or plate from a small structure to a large-sizedsound insulation wall.

INDUSTRIAL APPLICABILITY

According to the present invention, a light film member, and a framebody having at least one opening of a lattice, honeycomb or annularshape are provided, the periphery of the film member is secured by theframe body, and the section of the film member surrounded by the framebody is formed into a curved shape such as a dome and a barrel, whereinthe resonance frequency of the section in the in-plane stretchingvibration is set at a frequency equal to or higher than the audiblefrequency band, thereby being capable of insulating or absorbing soundby stiffness control.

Further, an elastic body and a film member are put on a supporting plateto be pressed with a frame body so that the elastic body and the filmmember are held between the frame body and the supporting plate to applya tensile force to the film member, wherein the film member is formedinto a curved shape such as dome, and the resonance frequency of thiscurved shape in the in-plane stretching is set at a frequency equal toor higher than the audible frequency band, thereby being capable ofinsulating or absorbing sound by stiffness control.

Still further, the film member or the plate member constituting thesound control.

Still further, the film member or the plate member constituting thesound insulation/absorption structure is provided with a piezoelectricmember and a circuit presenting a negative capacitance is connected tothe piezoelectric member. Further, the film member or the plate memberconstituting the sound insulation/absorption structure can be a memberwith piezoelectric properties. By connecting the circuit presenting thenegative capacitance to this member, it is possible to provide a soundinsulation/absorption device which can electrically control the soundinsulation/absorption performance.

The sound insulation/absorption structure and the soundinsulation/absorption device can be applied to all structures whichrequire sound insulation/absorption and to a member constituting thestructures, such as an automobile, a vehicle such as an electric train,an aircraft, a marine vessel and other transport equipment (vehicle), apanel, a partition and other building materials, a sound insulationwall, a sound-proof wall, a building structure, a chamber, electricequipment, a machine, acoustic equipment and the like.

1. A sound insulation/absorption structure having a film member formedof at least one of polymer and metal, wherein the film member is formedinto a curved shape such as a dome, a barrel, and a cone, a periphery ofthis curved shape is fixed to another structure, and a resonancefrequency of the curved shape in in-plane stretching is set at afrequency equal to or higher than an audible frequency band to insulateor absorb sound by elastic force of the film member.
 2. A soundinsulation/absorption structure comprising a film member formed of atleast one of polymer and metal, and a frame body having at least oneopening of a lattice, honeycomb or annular shape, wherein the filmmember is fixed to the frame body, a section of the film membersurrounded by the frame body is formed into a curved shape such as adome, a barrel, and a cone, and a resonance frequency of the curvedshape in in-plane stretching is set at a frequency equal to or higherthan an audible frequency band to insulate or absorb sound by elasticforce of the film member.
 3. The sound insulation/absorption structureaccording to claim 1 further comprising a holding means to hold the filmmember in the curved shape.
 4. The sound insulation/absorption structureaccording to claim 1, wherein a tensile force is applied to the filmmember.
 5. The sound insulation/absorption structure according to claim1, wherein the film member is replaced by a plate member, such as aplastic plate, a metal plate, and a veneer plate, molded into the curvedshape such as a dome, a barrel, and a cone.
 6. A soundinsulation/absorption structure comprising a film member, a frame body,an elastic body, and a supporting plate, wherein the elastic body andthe film member are disposed on the supporting plate to be pressed withthe frame body so that the elastic body and the film member are heldbetween the frame body and the supporting plate to apply a tensile forceto the film member, the film member is formed into a curved shape suchas a dome, and a resonance frequency of the curved shape in in-planestretching is set at a frequency equal to or higher than an audiblefrequency band to insulate or absorb sound by elastic force of the filmmember.
 7. A sound insulation/absorption structure comprising two filmmembers, a frame body, and an elastic body, wherein the elastic body isplaced between the two film members, the elastic body and the two filmmembers are held between the frame body to apply a tensile force to thetwo film members, the two film members are respectively formed into acurved shape, and a resonance frequency of the curved shape in in-planestretching is set at a frequency equal to or higher than an audiblefrequency band to insulate or absorb sound by elastic force of the film.8. The sound insulation/absorption structure according to claim 1,wherein the film member formed into a curved shape is set in aone-dimensional or two-dimensional array.
 9. The soundinsulation/absorption structure according to claim 1, wherein surfacedensity, elastic constant, outer peripheral dimensions, and curvatureradius of a curved section of the film member are set so that theresonance frequency of the curved shape in the in-plane stretchingvibration is within or higher than the audible frequency band.
 10. Thesound insulation/absorption structure according to claim 2, wherein thefilm member and the frame body are integrally formed.
 11. A soundinsulation/absorption device comprising the sound insulation/absorptionstructure according to claim 1, a piezoelectric member provided with thefilm member, and a circuit presenting a negative capacitance connectedto the piezoelectric member.
 12. The sound insulation/absorption devicecomprising the sound insulation/absorption structure according to claim1, wherein the film member thereof has piezoelectric characteristics,and a circuit presenting a negative capacitance is connected to the filmmember.
 13. A structure having the sound insulation/absorption structureaccording to claim 1 applied thereto, wherein the soundinsulation/absorption structure is applied to structures such as anautomobile, a vehicle such as an electric train, an aircraft, a marinevessel and other transport equipment (vehicle), a panel, a partition andother building material, a sound insulation wall, a sound-proof wall, abuilding structure, a chamber, electric equipment, a machine, andacoustic equipment to insulate or absorb sound.
 14. A memberconstituting the structure having the sound insulation/absorptionstructure according to claim 2 applied thereto, wherein the soundinsulation/absorption structure is applied to a member constituting thestructure such as an automobile, a vehicle such as an electric train, anaircraft, a marine vessel and other transport equipment (vehicle), apanel, a partition and other building material, a sound insulation wall,a sound-proof wall, a building structure, a chamber, electric equipment,a machine, and acoustic equipment to insulate or absorb sound.
 15. Astructure having the sound insulation/absorption device according toclaim 11 applied thereto, wherein the sound insulation/absorption deviceis applied to the structure such as an automobile, a vehicle such as anelectric train, an aircraft, a marine vessel and other transportequipment (vehicle), a panel, a partition and other building material, asound insulation wall, a sound-proof wall, a building structure, achamber, electric equipment, a machine, and acoustic equipment toinsulate or absorb sound.
 16. A member constituting the structure havingthe sound insulation/absorption device according to claim 12 appliedthereto, wherein the sound insulation/absorption device is applied tothe member constituting the structure such as an automobile, a vehiclesuch as an electric train, an aircraft, a marine vessel and othertransport equipment (vehicle), a panel, a partition and other buildingmaterial, a sound insulation wall, a sound-proof wall, a buildingstructure, a chamber, electric equipment, a machine, and acousticequipment to insulate or absorb sound.
 17. The soundinsulation/absorption structure according to claim 2, further comprisinga holder to hold the film member in the curved shape.
 18. The soundinsulation/absorption structure according to claim 2, wherein a tensileforce is applied to the film member.
 19. The sound insulation/absorptionstructure according to claim 2, wherein the film member formed into acurved shape is set in a one-dimensional or two-dimensional array. 20.The sound insulation/absorption structure according to claim 2, whereinsurface density, elastic constant, outer peripheral dimensions, andcurvature radius of a curved section of the film member are set so thatthe resonance frequency of the curved shape in the in-plane stretchingvibration is within or higher than the audible frequency band.